configure: enable the drm pipe-loader for non swrast drivers

configure: enable the drm pipe-loader for non swrast drivers

All hardware drivers including the virtual vmwgfx require
the drm pipe-loader in order to be properly loaded by xa,
gbm and opencl.

Note this does _not_ add support for the above three it only
allows the pipe driver to be loaded by the library.

Eg. GBM will now properly open the pipe-i915 driver, should
one be working on the such hardware.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75453
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>